The following error message say that Gmail checked your forwarded email and found it to be SPAM
Subject: Delivery Failure
Could not deliver message to the following recipient(s):
Failed Recipient: email@example.com
Reason: Remote host said: 550 5.7.1 information. a54si3234084qtc.355 - gsm
If the email-sending domain's SPF record does not specifically allow yourdomain.com as an intermediary forwarder, then such forwarded-email will fail SPAM check and bounce. As it is not possible to control SPF record of 3rd party email senders, the correct way is to change your email-collection process to comply with current Anti-SPAM systems.
We recommend that you stop email auto-forwarding at yourdomain.com, instead at Gmail goto Settings >> Account and Import >> Check mail from other accounts >> Add a mail account
and setup email-collection by Gmail from yourdomain.com.